Photography
Lecture Note: Exposure
Exposure Lecture Outline
I. Why the need for meter exposure readings?
A. The energy differences between the darkest areas one can see into and the areas of brightest
light (where one can still tell that one source of light is brighter than another) is well
beyond the tonal range a film can record.
B. A meter is then necessary to find the best compromises to allow maximum use of a film's
limited response to light energies.
C. The goal of the metering technologies is to give the photographer the exposure settings
which will record that area of the view analyzed by the meter to be rendered on the film as
the middle tonality/color, or the "medium gray" when photographing in black and white.
II. For the camera meter to determine proper exposure, it must have four pieces of information.
A.. Light intensity of the light illuminating the subject
B. Film speed or film’s sensitivity to light
C. Shutter speed or exposure time
D. aperture or lens' setting for size of its opening (the “f/stop”)
III. For a given film, a well defined amount of light energy is specified to achieve "Proper Exposure".
A. The amount of light required by a film to make an exposure (the film's sensitivity to light)
is denoted by the ISO or ASA number rating.
1. The higher the ISO number, more sensitive the film (film needs less light to make an exposure).
a. The ISO number is the "film speed"
b. ISO = International Standards Organization, ASA = American Standards Association.
1) In Europe, films are rated either by ISO numbers, or the DIN (German)
numbering system.
B. Analogy: when pouring water into a glass, a certain amount of water is needed to "fill" the glass.
"Proper exposure" is represented by a full glass.
1. When a film receives enough light, it makes a "proper exposure".
2. The glass can be filled with water in different ways: quickly, slowly, incrementally.
3. Films can be given proper exposure by different ways too.
a. Pictures taken with flashes, long exposures to dim light, multiple exposures, etc.
b. Too much light = Overexposure, too little light = Underexposure.
IV. The duration of time that films are exposed to light is control by camera's shutter.
A. Duration of time is incremental, set by the "shutter's speed”
1. Usual increments are based on fractions of a second
a. 1 second, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, and so on.
b. Likewise, speeds greater than a second are 1 sec., 2 sec., 4 sec., 8 sec.,etc.
B. Each increment is either 2x or 1/2 the amount between successive steps
C. Special shutter speed found on some cameras is the setting labeled "B" (from bulb).
1. This is the manually controlled shutter "speed"; shutter remains open as long as the
shutter release button is depressed. Used with a cable release to avoid camera shake.
a. Used to make very long exposures: several seconds to many hours.
D. Camera or Hand shake: the most common source of blurry pictures is not being able to
hold camera steady while taking the pictures.
1. Problem arises when using a too slow of a shutter speed.
2. Use fast shutter speeds like 1/125, 1/250, 1/500 or faster if possible.
a. General guideline for slowest allowable shutter speed:
speed = 1/(focal length of lens in mm) ___ see below for definitions of focal
length.
A. Takayama
Oct/2006
Photography
Lecture Note: Exposure
V. Lens opening is called the lens' aperture
A. Opening controlled by the lens' "diaphragm", a set of metal blades inside the lens. Size
of opening is adjusted with the "f/stop" ring.
B. F/stops are a mathematical relationship of the focal length of a lens and the size of the
lens opening or aperture.
1. Thus actual numbers are independent of any particular lens.
a. f/stop defined as focal length (in millimeters or mm) of lens divided by diameter of
lens opening (again in mm).
b. Focal length is defined as the distance between optical center of lens and the
position of the focused image of a subject at an infinite distance.
1) Most focal lengths expressed in millimeters (mm).
2) Example: for the 50mm lens found on most 35mm cameras, when lens is focused on a
star, the distance between lens' center and the film will be 50 mm.
a) A 50 mm lens set at f/2 means the lens opening is 25 mm in diameter.
f/stop = focal length = 50 mm = f/2
lens opening 25 mm
C. The actual sequence of f/stop numbers is not standardized, but most start at f/1.0.
1. The sequence used most often is set up so each increment between sequential f/stops is
either two times (2X) or one_half (1/2) the size of the next f/stop.
2. f/stop sequence: f/1 f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22
a. The size of the lens opening @I<decreases> with each larger f/stop number.
1.) Examples:
f/2 is 2x as large as f/2.8
f/8 is 2x as large as f/11
f/2 is 1/2x as large as f/1.4
f/8 is 1/2x as large as f/5.6
D. The increment between the each whole step of f/stops is called "1/stop"
1. Using the glass of water analogy, f/stops could represent the size of a funnel used to
pour water into glass.
a. A funnel with opening of "size f/2" would allow twice the amount of water
to flow, as a funnel of "size f/2.8"
b. If glass took 1 second to fill with "f/2 funnel", it would then take 2 seconds to
fill with "f/2.8 funnel"
2. So to get "proper" exposure, there is a certain time required for each f/stop.
VI. 1/stop Difference in exposure: from a given initial exposure setting, any change in settings
which is a change of 1/2X or 2X as much exposure.
A. Changing shutter speed one increment is a 1/stop change. Example: changing from 1/30 sec.
to 1/60 sec. (1/2X), or changing 1/500 sec. to 1/250 sec. (2X) are both 1/stop changes.
B. Changing f/stops one increment is a 1/stop change. Example: changing f/4 to f/5.6 (1/2X),
or f/11 to f/8 (2X) are both 1/stop changes.
VII. Proper exposure is then choosing a combination of f/stops and shutter speeds to get enough
light to make the desired exposure.
A. Overexposure: too much light (over_filling the glass of water) will cause too much exposure.
B. Underexposure: too little light (not enough to fill glass) will cause too little exposure.
A. Takayama
Oct/2006
Photography
Lecture Note: Exposure
VIII. "Sunny Sixteen Rule:" generalized exposure calculation for taking pictures outdoors
A. Rule applies only for pictures taken at mid_day (10AM _ 3PM) for subjects in
direct sunlight. Exposure directions as follows:
1. Must have film speed number (ISO #). Example: for Ektachrome 100: ISO rating is 100.
2. Shutter speed will be at 1/(ISO #). Thus for ISO 100, shutter speed is 1/100 sec.
a. For practical purposes, use the nearest shutter speed available;
for most cameras a speed of 1/125 is used for 1/100, 1/250 for IS0 200, 1/60 for IS0 64, etc.
3. The lens is set at f/16.
4. It's possible to estimate exposures for subjects in shade, usually 2/stop more exposure needed.
These "rules" were often used prior to availability of built_in light meters.
IX. Reciprocal exposures = equivalent exposures; combinations of different shutter speeds and
f/stops giving the same exposure to the film
A. Again, for any give film, there is only one "proper exposure" = the amount of light necessary to
make a satisfactory image on the film
B. There are different combinations of lens aperture and shutter speeds which will give you
the same amount of light on the film.
C. The light meter will return a set of lens settings (f/stop) and shutter speed which will
render whatever light was measured as the middle gray or tonality of the picture.
1. For instance: for a picture in direct sunlight with an film with a speed of
ISO 100, the exposure will be f/16 at 1/125th second.
2. A reciprocal exposures of f/16 @ 1/125 could be:
f/11 @ 1/25
f/8 @ 1/500
f/5.6 @ 1/1000
f/4 @ 1/2000
f/22 @ 1/60
f/32 @ 1/30** (Be careful of shutter speeds below 1/60 to
avoid hand shake or camera shake.)
B. Calculating reciprocal exposures
1. Recall f/stops are in increments of 2x or 1/2x for each 1/stop difference
2. Shutter speeds are also spaced out in 2x or 1/2x increments or in "1/stop" increments.
3. So a change in one value of f/stops requires an opposite change in shutter speed to
maintain equivalent exposures.
a. Examples:
1). Start with exposure at f/8 at 1/125. If change f/8 to f/11, change is 1/stop
less exposure. So a change in shutter speed is needed to compensate.
Then shutter speed is changed to 1/60, to give 1/stop more exposure by time.
The result is an equivalent exposure.
2). Again, start with exposure at f/8 at 1/125. If change 1/125 to 1/250, change is
1/stop less exposure. Change f/stop to compensate: change f/8 to f/5.6 for a
1/stop increase in light passing through the lens. Result is an equivalent
exposure with a different set of lens aperture and shutter speed.
D. Films have a defect called reciprocity failure.
1. When shutters speeds are shorter than 1/1000th second or longer than one second,
equivalent exposures do not work. Film speed appears to slow down, resulting in
underexposure.
A. Takayama
Oct/2006
Photography
Lecture Note: Exposure
SELECTION OF EXPOSURE OPTIONS
Selection of Aperture as a Priority:
I. Lens aperture controls Depth of Field (d.o.f.)
A. Depth of field is the range of distances from the camera in which the image appears
to be in-focus. Actually, in a photograph, the only subject truly in-focus is the
subject the camera's lens was focused on. Everything else is in various degrees of
out-of-focus. The further away something is in distance in front of or behind the
subject focused on, the more it will appear to be out-of-focus.
B. A large range of distances which appears in-focus is a great depth of field.
This is achieved with the lens aperture at f/11, f/16, f/22, etc.
These are the smallest lens apertures or lens openings.
1. The extreme great d.o.f. is achieved with a "pin-hole" camera. This is a camera
with an aperture the size of a hole made with a needle. In the picture,
everything is of equal focus sharpness. Actually, everything is equally "fuzzy"
as nothing is truly in-focus, everything is in soft-focus.
C. A very limited range of distances which appear in-focus is a shallow depth of field.
This is achieved with a lens aperture at f/4, f/2.8, f/2, etc. These are the largest
lens openings.
1. The use of a limited depth of field to isolate your subject from the rest of the
image is called selective focus. This is a picture in which the subject you
focused on will be the only thing in-focus. Everything in front of or behind the
subject will be out-of-focus.
Selection of Shutter Speed as a Priority:
I. Selection of shutter speed for depiction of motion in a still photograph
A. The selection of shutter speed is used to show something is in motion. There are three
types of "motion" pictures:
1. Freeze frame or Stop Action. The subject that is in motion is frozen in
time, or stopped in mid_action. This is commonly used in pictures of sports
action, dancers, animals running or flying, to freeze a stream of water,
to catch any scene that's "quicker than the eye."
a. Must use a shutter speed faster than 1/500th of a second: 1/500,
1/1000, 1/2000, the faster the better.
b. Note: Most electronic flashes produce burst of light which are very
short in time. Typically, flashes last around 1/400th to 1/800th second.
Hence, flash pictures qualify as "stop action" pictures.
2. Blurred motion. In these pictures, only the subject is blurred; as
opposed to having the entire picture blurred. Therefore, the subject is blurred
but everything else in the picture is clear.
a. Use a slow shutter speed,> like 1/15, 1/8, 1/4, 1/2 second. Be sure
to support or brace the camera for these long exposure times, otherwise
you will experience camera shake and the whole picture will be blurry
A. Takayama
Oct/2006
Photography
Lecture Note: Exposure
3. Panned pictures. A special type of blurred image in which the subject is in
relatively good focus and the background is streaked. The streaked background
is the key feature of this technique, as it is what makes the image "move".
If the background is just blurred or out_of_focus, the image might be just
a shallow depth_of_field picture.
a. Use a slow shutter speed like a blurred motion picture: 1/30, 1/15,
1/8, 1/4, etc. However, to have the subject in_focus, you must move the
camera to follow the subject as it moves across your field of view.
The degree you are able to follow the subject, to keep the subject in the
same position in the camera's viewfinder, the clearer it will appear in
the final picture. The hard part is to take the picture as you follow
the subject. You must not stop following the subject as you take the
picture. This is difficult with many cameras as the viewfinder goes
dark when you take the picture.
BRACKETING EXPOSURES
The following instructions are procedures for altering the exposures used in making your photograph.
The "normal" exposures are the usual camera settings based upon the camera's meter system responses to
lighting and other variables of picture taking. Bracketing means to intentionally change the exposure to
get lighter or darker than normal images.
I.. Overexposure, to give image more exposure (final result is a lighter than normal image):
Bracketing for 1/stop MORE exposure: Using the camera's meter "normal" reading as a starting
point, either decrease shutter speed one step (like 1/125 to1/60) or open the lens aperture one
increment more. Remember, the numbers for f/stops on the lens go backward. So to open the lens
one stop would mean moving the aperture control to the next lower number (like changing f/8 to
f/5.6).
When changing shutter speeds, remember to pay attention to problems of using speed below 1/60th
second. It's always wise to find some type of support to brace yourself or your camera to avoid
"camera shake" during slower exposure times.
II. Underexposure, to give image less exposure, (final result is a darker than normal image:
Bracketing for 1/stop LESS exposure: Using the camera's "normal" meter reading as a starting point,
either increase shutter speed one step, or close down the lens aperture one increment (go to the next
higher number setting).
In many situations, such as in dramatic lighting conditions, it is often advantageous to bracket the
normal exposure with even greater variation than_1/stop. Try _2/stops and _3/stops exposures that
are darker than normal. For extremely dramatic sunset images, it is not unusual to try exposures that
are_4/stops or even _5/stops darker than normal. Naturally the landscape will be very dark, even
black out, but the sun and the surrounding sky will be more colorful.
A. Takayama
Oct/2006
Photography
Lecture Note: Exposure
Important: When "bracketing" exposures, just change one control; either the shutter speed or lens
aperture. Changing both could get very confusing.
If your camera has automatic exposure controls, manually changing the exposures will usually make the
camera signal an error in exposure. Disregard the signals, and just shoot at the manual settings.
If you have an automatic camera with built_in bracketing adjustments, making bracketed exposures is
greatly simplified. The "normal" setting for exposure compensation is most often indicated as "0", "1X",
or "off". To bracket, you are to set the exposure control to "2X" or "+1" to make a 1/stop lighter picture.
Similarly, set the control to "1/2X" or "_1" to make a 1/stop darker picture. If in doubt, consult your
camera's operations manual.
Again, always check which shutter speeds you are using, to remind yourself to take precautions against
possible camera shake if necessary.
A. Takayama
Oct/2006